The inside of a warehouse where a fire claimed the lives of at least thirty-six people is seen on December 5, 2016 in Oakland, California. The fire took place during a musical event late Friday night. (Photo by Elijah Nouvelage/Getty Images) (Photo: Elijah Nouvelage, 2016 Getty Images)

OAKLAND, CALIF. (AP) - A man who illegally rented out space in an Oakland, California, warehouse that caught fire and killed 36 people has been arrested and will be charged with involuntary manslaughter along with the organizer of a party at the site, a source close to the investigation told The Associated Press on Monday.

The Alameda County district attorney says she will formally announce charges later in the day.

The specific cause of fire will likely never be known, the prosecutor said.

The person says Derick Almena and Max Harris will each be charged with 36 counts of involuntary manslaughter. The source was not authorized to publicly discuss the charges and spoke on condition of anonymity.

Authorities say Almena leased the warehouse and illegally sublet space for artists to live and work. He is also accused of holding for-profit concerts at the warehouse, which was not licensed for entertainment.

Harris lived at the Ghost Ship and is accused of helping plan the December concert where the fire broke out. The building was licensed as a warehouse only and not for entertainment or residency.

More than six months after the fatal blaze, authorities have not disclosed what caused the fire but have said they are investigating electrical causes.

Kyndra Miller and Jeffrey Krasnoff, attorneys who represent Almena, did not immediately return phone messages Monday. It's not known if Harris is represented by an attorney.

Oakland city records show neighbors, residents and visitors repeatedly complained about the warehouse to city officials, citing safety problems, loud parties and other issues with the dilapidated building that had been illegally converted into a living spaces.

Firefighters and other city officials also were called to the property and adjacent buildings. No citations were issued.

Relatives of half the victims who died in the fire have filed wrongful death lawsuits against Chor Nar Siu Ng, the building's owner, and Almena, who held the lease. The lawsuits also name Pacific Gas & Electric, alleging the utility should have known the warehouse was wired hazardously.